Switch mechanisms for electrically operated hoist



Oct. 2, 1962 A. T. c. BURROWS 3,056,586

SWITCH MECHANISMS FOR ELECTRICALLY OPERATED HOIST Filed June 13, 1960 2 Sheets-Sheet l Oct. 2, 1962 A. T. c. BURROWS SWITCH MECHANISMS FOR ELECTRICALLY OPERATED HOIST Filed June 13, 1960 2 Sheets-Sheet 2 United States atent assignor t Geo. W. King Limited, Stevenage, England, a British company Filed June 13, 1960, Ser. No. 35,520 Claims priority, application Great Britain June 17, 1959 3 Claims. (Cl. 254168) This invention relates to switch mechanisms adapted for use with electrically operated hoist pulley blocks. The pulley blocks are of the type employing two chain guards which are disposed about the hoist sprocket and are sup ported for independent displacement. The guards may be displaced as a result of contact with abutments carried by the hoist chain or as a result of the approach towards the sprocket of a kinked, twisted or otherwise distorted portion of the chain.

According to the invention in a hoist pulley block incorporating two chain guards of the kind above referred to a switch mechanism is provided to effect cutting off of the flow of electrical power to hoist motor in the event of displacement of either of said guards from its operative position. Such mechanism comprises two electrical switches disposed in the motor circuit each having an actuating element. The switches each further include a rigid arm adapted to cooperate with each of said elements. A spring urges the rigid arms out of contact with said actuating elements thereby to effect opening of the switches. There is additionally provided means for holding the arms in contact with said elements when the chain guards are in their operative position. Moreover, on displacement of either of the guards the means is rendered ineffective whereby one of said arms will be allowed to move under the action of the resilient means thereby to cause opening of the switch with which it is associated and stoppage of the hoist.

In order that the said invention may be more clearly understood and readily carried into effect the same will be hereinafter more fully described with reference to the accompanying drawings in which:

FIGURE 1 shows in side elevation a chain guard assembly for use in an electrically operated hoist of known type, certain parts being removed to permit clearer illustration,

FIGURE 2 is a plan view of the mechanism shown in FIGURE 1,

FIGURE 3 is a side elevational view showing an arrangement of limit switches for controlling the hoist motor,

FIGURE 4 is an end view looking from the left of FIGURE 3.

Referring now to the drawings and 11 denote chain guards which are in known manner disposed about the chain sprocket of an electrically operated hoist. In FIGURE 1 the hoist sprocket is indicated in dotted lines at 12 and it will be seen that the guards 10 and 11 cover the portions of the hoist chain passing around the sprocket. The guards are pivoted respectively at 13 and 14 and are urged into operative or guard positions by springs 15. Such a guard arrangement is generally well known and is described for example in US. Patent 2,429,- 084. In a hoist incorporating such a chain guard it is common practice to provide on the hoist chain at selected points so-called limit stops or abutments which project from the chain and are adapted as the latter approaches the limit of its travel in either direction to contact one or other of said guards thereby to cause displacement of the latter against the action of the aforesaid springs 15. The arrangement is also such that one or other of the ice guards 10, 11 will also be displaced in the event that any section of the chain approaching the hoist sprocket becomes kinked, twisted or otherwise distorted.

In the present case it is proposed to provide means which will be effective on displacement of either of the guards 1t 11 to cause automatic cutting off of the hoist motor. To this end there is coupled to the upper part of the guard 10 a bar 16 and to the upper part of the guard 11 a pair of bars 17. Bars 16, 17 are arranged in parallel relationship and project to one side of the hoist sprocket in a substantially horizontal plane. The single bar 16 which is connected to the guard 10 is located between the other two bars 17, and passes through a slot in a vertical link 18 which is fixedly mounted on shaft 19 disposed below and extending transversely with respect to the bar. Located on the bar 16 in spaced relation one at each side of link 18 are two laterally projecting abutments 20 the purpose of which will be hereinafter made apparent. The pair of bars 17 associated with the second guard 11 each pass through a slot in a separate vertical link 21, 22. Links 21, 22 are fixedly mounted on a second shaft 23 which is disposed below the bars 17 and which extends transversely thereto and parallel to the first shaft 19'. Each of the bars 17 is provided with two laterally projecting abutments 24 adapted to cooperate with the respective links 21, 22 as will be hereinafter more fully described.

As indicated above, the two shafts 19, 23 which may conveniently be of rectangular section as shown are disposed in spaced parallel relation and the shaft 19 in addition to carrying a single vertical link 18 carries an arm 25 which is adapted to cooperate with a movable contact element of a switch 26, disposed in the hoist motor circuit. Similarly the shaft 23 in addition to carrying the two links 21, 22 also carries an arm 27 which is adapted to cooperate with a movable contact element of a switch 28 also located in the hoist motor circuit. Interposed between the two arms 25, 27 is a compression spring 29 which tends to force the arms apart into a position such that they will be out of contact with their respective contact elements. In the normal or operative positions of the guards the bars 16, 17 are positioned as shown in FIGURE 2 such that one of the abutments 20, i.e. the left abutment on the bar 16 in FIG. 2 and one of the abutments 24, i.e. the right abutments on each of the bars 17 will be in contact with their respective links 18, 21, 22 and will hold the latter against angular displacement such as would normally take place by virtue of the action of the compression spring 29, interposed between. the aforesaid arms 25, 27 on the two shafts 19, 23. In this position the arms 25, 27 will be held in their operative positions in contact with the respective contact elements of the two switches 26, 28 so that the motor circuit will be closed. In the event of displacement of one of the guards the single bar 16 or the pair of bars 17 as the case may be will be displaced longitudinally to displace the respective abutment 20 or abutments 24 whereby the appropriate vertical link 18 or links 21, 22 will be free for angular displacement. Upon displacement of the bars 16, 17 the spring 29 interposed between the two arms 25, 27 carried by the shafts 19, 23 will be efiective to pivot the appropriate arm to cause the same to move out of contact with the contact member of he appropriate switch thereby to open the motor circuit. For example assuming that the first guard 10 is displaced then the single bar 16 will move longitudinally to the left as shown, the left hand abutment 20 being displaced and no longer effective to hold the vertical link 18 against angular displacement. By reason of the action of the spring 29 interposed between the arms 25, 27 on the two shafts the arms 25 carried by the shaft 19 will be pivoted thereby to bring it out of contact with the contact element of the switch 26.

It may be pointed out that the tension springs 15 interconnecting the guards 10, 11 will be stronger than the spring 29 interposed between the arms 25, 27 on the shafts 19, 23 so that the contactswill normally be maintained closed so long as the guards 10, 11 are in their operative positions ice. the spring 29- between the arms will be ineffective to cause displacement of the bars 16, 17 against the action of the spring 15.

What I claim is:

1. In an electrically operated hoist having a sprocket driven by electrical means and a chain engaging said sprocket and driven thereby, the provision of a switch mechanism for selectively interrupting operation of said electrical means, the switch mechanism comprising two chain guards pivotably supported adjacent said sprocket and adapted to fit around said chain as the same passes around said sprocket, an actuating bar coupled to each of said chain guards and displaceable in response to pivotal movement of the associated chain guard, resilient means urging said chain guards to assume a first operative position, two switches each adapted for selectively interrupting flow of electrical power to said electrical means, each switch including a movable contact constituted by a rigid arm, a shaft connected to each said arm, means operatively connecting the bars to respective shafts to hold the latter in position corresponding to closed position of the switches with the chain guards in operative position, and a spring coupled to said arms and urging the same to open position of the switches, the last said means being ineffective to hold a respective shaft in position upon pivotal movement of a corresponding chain guard, whereby said spring urges the associated arm on said shaft to an open position of said switch thereby interrupting the flow of electrical power to said electrical means.

2. A switch mechanism as claimed in claim 1, wherein the means operatively connecting the bars to the shafts includes a link rigidly supported on each shaft, each link being provided with a slot, a corresponding one of said bars being slidably supported in the slot in each link, and in abutment on each bar for engaging and holding the corresponding link and shaft in a position corresponding to closed position of the associated switch with the chain guards in said first position.

3. A switch mechanism as claimed in claim 2, wherein the actuating bars extend substantially parallel to one another, and the shafts extend transversely of the bars in parallel fashion. I

References Cited in the file of this patent UNITED STATES PATENTS 

